Conventional optical modules, such as the wavelength division multiplexing (WDM) centerpieces 1a and 1b disclosed in FIGS. 1 and 2, respectively, include an input fiber 2 and a first output fiber 3 encased in a double-bore fiber tube ferrule 4, and optically coupled to a collimating lens 6, which collimates a beam of light launched from the input fiber 3 onto a WDM filter 7. Typically, the WDM filter 7 is designed to pass one or more selected wavelength channels to a focusing lens 8, while reflecting the remaining wavelength channels back through the lens 6 to the first output fiber 3. The focusing lens 8 focuses the transmitted light onto a second output fiber 9, which is encased in a fiber tube ferrule 11.
One method of assembling the elements of the centerpiece, illustrated in FIG. 1, includes gluing all of the interfaces 12 together with an adhesive selected to bind glass elements together. The aforementioned method is relatively labor intensive and results in adhesive in the optical path.
In an effort to automate the assembly process and eliminate the need for adhesive in the optical path a method involving metal, e.g. stainless steel, sleeves was developed. FIG. 2 illustrates this method, in which the ferrules 4 and 11, and the lenses 6 and 8 are secured in metal sleeves 13, which get fixed together by solder or welds 14. Unfortunately, inconsistencies develop in the welding process, in particular misalignment caused by post weld shifting of the elements.
A conventional optical component, i.e. an erbium doped fiber amplifier (EDFA), is illustrated in FIG. 3, and includes as many as eleven discrete modules coupled together by as many as twelve different splices 20. An input fiber 21 launches a main signal to be amplified through a first tap coupler 22, which directs a portion of the main signal to an initial photodiode receiver 23. Isolators 24 ensures light does not travel backward through the system. WDM centerpieces 26, such as the ones illustrated in FIGS. 1 and 2, transmit the main signal through the erbium doped fiber 27 for amplification, while reflecting pumping signals from pump lasers 28 therethrough. A second tap coupler 29 directs a portion of the amplified signal to a final photodiode 31 for gain measurement and control. It is quite evident from this design that the assembly process would be quite labor intensive, and that the number of splices 20 provide numerous opportunities for excess losses.
An object of the present invention is to overcome the shortcomings of the prior art by providing a simplified module incorporating several functions which is itself a part of a larger component.